Current vehicles, such as heavy-duty class 8 trucks for traveling along highways and other roadways are understood to be designed to haul the gross vehicle weight rated (GVWR) loads while operating on the steepest realistic grade, which represents the worst-case scenario. Hence, engines for such vehicles are specified with a maximum torque curve suitable to propel the truck or other vehicle in the above-mentioned worst-case scenario. This maximum torque curve is typically programmed into an engine control unit (ECU) and for convenience is sometimes referred to herein as the Max Torque Curve. In conventional trucks, a driver moves a throttle pedal during operation of a vehicle. Electronic throttle pedals commonly being used in today's trucks transform a driver's throttle pedal request (based on the position of the throttle pedal during vehicle operation) to an engine torque request, which is then limited by the Max Torque Curve programmed into the ECU. For example, if the throttle pedal request is for a greater amount of torque than permitted by the Max Torque Curve at the engine speed, the torque is limited to the maximum torque allowed by the Max Torque Curve and not a greater torque corresponding to the throttle pedal request.
A conventional engine controller schematic in accordance with this known approach is depicted in FIG. 1. In FIG. 1, an electronic accelerator pedal control 10 is shown with an accelerator pedal 12. A signal 14 corresponding to the accelerator pedal position is delivered to an engine controller 16 for the vehicle engine. At block 20 of the engine controller, a driver's accelerator pedal percentage request (based on the position of the accelerator pedal 12) is converted to an equivalent percentage torque request. This mapping incorporates any applicable throttle pedal filtering in a conventional manner. The requested percentage torque signal 24 is then used to calculate the requested vehicle torque, which is limited by the Max Torque Curve 26 to not exceed the maximum torque permitted by the Max Torque Curve. A signal indicating the desired torque is shown at 28 in FIG. 1 and corresponds to the desired torque if the requested torque is less than the maximum torque permitted by the Max Torque Curve, or to the maximum torque if the requested torque is greater than the torque permitted by the Max Torque Curve. Based on the requested torque signal 28, and the current engine speed, the engine controller 16 calculates the amount of fuel to be injected into or otherwise delivered to the cylinders of the engine. This calculation can be performed in a conventional manner utilizing a fuel map 30 as shown in FIG. 1.
In essence, as long as the driver's request for acceleration does not exceed the maximum torque permitted by the Max Torque Curve, the request for acceleration is granted irrespective of the load on the engine, which load significantly varies with factors such as the vehicle mass and road grade. For example, a vehicle traveling on a flat road with no cargo is operating at a very low engine load in comparison to a fully loaded vehicle traveling on a steep grade. Consequently, when a vehicle is traveling unloaded on a flat road and a vehicle cruise control, if any is present, is inactive (meaning the cruise control is not being used to control the vehicle even if technically on), the vehicle driver/operator can accelerate on an irregular basis to the maximum limit dictated by the Max Torque Curve, which can result in wasted fuel due to unnecessary or unregulated rates of acceleration of the vehicle limited only by the Max Torque Curve.
It is not unusual for a Class 8 heavy duty truck to operate under cruise control for approximately 50% of the time. Under active cruise control, the driver/operator is not actively controlling the vehicle's speed with the cruise control requesting the necessary engine torque to maintain a steady speed. Under cruise control, the vehicle experiences low rates of acceleration and deceleration. It is not unusual for a truck of this type to be operating under idle conditions for approximately 20% of the time and thus is under minimal torque conditions. It is also not uncommon for approximately 30% of the time for the vehicle to be actively controlled by the driver/operator with the driver/operator constantly operating the accelerator pedal to move the vehicle. Depending upon the expertise of the driver, the vehicle could experience varying rates of acceleration while traversing the same route from point A to point B. A good, fuel-efficient driver tries to maintain low rates of acceleration by requesting less torque from the accelerator pedal thereby saving fuel. An inexperienced driver could be aggressive and accelerate and decelerate the vehicle, leading to a fuel penalty (wasted fuel and low mileage). The unregulated rate of acceleration of the vehicle, other than by the Max Torque Curve, can thereby contribute to fuel penalties.
Therefore, a need exists for improved vehicle torque management whereby a driver's request for acceleration is limited depending upon conditions such as engine loading conditions, environmental conditions and vehicle operating parameters. This can improve the fuel efficiency achieved by drivers, especially aggressive and inexperienced drivers.